深水浅层安全钻井液密度窗口预测技术及工程应用

The technology for predicting the safety density window of drilling fluid in deepwater shallow layers and its engineering application

深水浅部地层成岩性差,井眼易塌、易漏,钻井液安全密度窗口窄,安全钻井液密度窗口的精确预测是深水钻井作业安全和成功的关键。通过分析水深浅部地层地应力、成岩特征,提出了深水地层密度分段预测方法,并据此确定了深水井的3个地应力纵向剖面(上覆岩层压力、水平最大地应力和水平最小地应力);建立了深水浅层塑性地层井壁坍塌压力极限应变计算模型,实现了深水浅层安全钻井液密度窗口的精确预测,并在西非赤道几内亚湾深水S1井进行了应用,确定了S1井的钻井液安全密度窗口,保障了该深水井的安全快速钻井。

The shallow formations in deep water are of poor diagenesis,so the wellbores tend to suffer collapse and leakage easily and the safety density window of drilling fluid is narrow.For this,the precise prediction on the safety density window of drilling fluid is key to the safety and success of deepwater well drilling operation.The segmented prediction method for deepwater formation density was put forward by analyzing the in-situ stress and lithologic and diagenetic characteristics of shallow formations in deep water.And accordingly,the vertical profiles of three in-situ stresses(overburden pressure,maximum horizontal in-situ stress and minimum horizontal in-situ stress)in deepwater wells were determined.Then,the model for calculating the ultimate strain of the wellbore collapse pressure in deepwater shallow plastic formations was established.And by virtue of this model,the safety density window of drilling fluid in the deepwater shallow formations can be predicted precisely.What’s more,it was applied in the deepwater well(Well S1)which is located in the Gulf of Equatorial Guinea in West Africa.And owing to its application,the safety density window of drilling fluid in Well S1 is determined and the safe and fast drilling of Well S1 is guaranteed.